Herpes Zoster (HZ) is estimated to affect between 600,000 to 1 million people annually in the United States. The incidence and severity of HZ, as well as the frequency and severity of its complications, increase markedly with age. Antiviral therapy has modest impact on the acute phase of HZ. However, it does not appear to prevent post herpetic neuralgia, the most common complications of HZ. Studies during the past decade have revealed a close temporal relation between the age-related increase in the incidence and severity of HZ and an age-related decline in cell mediated immunity to varicella-zoster virus (VZV). The administration of a live attenuated varicella-zoster vaccine to older adults results in a marked and long lasting increase in VZV-specific cell-mediated immunity. We hypothesize that by boosting VZV-specific cellular immune responses, the incidence and severity of HZ and its complications can be reduced. This a double-blind, placebo-controlled multicenter trial to determine whether immunization with a live attenuated varicella-zoster virus vaccine decreases the incidence and severity of HZ and its complications in adults 60 years of age and older. Approximately 37,200 subjects will be randomized to receive either the vaccine or placebo. Of these, 1,800 will be enrolled at the NIH Clinical Center. Subjects who develop HZ will be evaluated for severity and duration of the associated pain, extend and duration of the rash and changes in quality of life associated with the disease. As of August 25, 2,000, 946 volunteers have been enrolled at the NIH Clinical Center and 20,719 subjects have been vaccinated nationwide. To date, two confirmed cases of HZ have occurred at our site. The Data Safety and Monitoring Board (DSMB) is meeting on regular basis and at its last meeting on June 18, 2000, the board concluded that the distributions of serious adverse experiences by treatment group (vaccine vs placebo) did not suggest any vaccine related safety problems